Vacuum ultraviolet excited green phosphor material and light-emitting device using the same

ABSTRACT

This invention is intended to overcome the problems with conventional phosphor materials, specifically to overcome the problems of insufficient luminance and of color impurity on the screens of color display units when green phosphor materials have blue or red light emission. This invention is intended to provide vacuum ultraviolet excited green phosphor materials that include terbium, gadolinium-doped rare-earth aluminum scandium borate represented by the following general formula: (Y 1-x-y Gd x Tb y )Al 3-z Sc z (BO 3 ) 4  (0≦x&lt;0.5, 0&lt;y&lt;0.5, 0&lt;z≦3). The phosphor materials of this invention can be used for light-emitting devices. Using the phosphor materials in combination with blue phosphor materials and red phosphor materials enables the formation of white emitting device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a vacuum ultraviolet excited green phosphormaterial and a light-emitting device using the same.

2. Description of the Related Art

At the present time, fluorescent lamps containing mercury are in commonuse as illumination. This mercury vapor lamp generates ultravioletradiation using mercury vapor discharge and then causes 3 phosphormaterials, R (red: red wavelength region with peak emission wavelengthof 600 to 615 nm), G (green: green wavelength region with peak emissionwavelength of 535 to 570 nm) and B (blue: blue wavelength region withpeak emission wavelength of 440 to 470 nm) (hereinafter abbreviated asR.G.B), to emit light to illuminate a white fluorescent lamp. However,these fluorescent lamps use in their inside mercury harmful to theenvironment and therefore the development of mercury-free fluorescentlamps, which use rare gases such as xenon, are being actively pursued.The mercury-free fluorescent lamps containing xenon gas emit vacuumultraviolet light using xenon discharge and cause the phosphor materialsof 3 colors, R. G. B, to emit light to yield white light.

On the other hand, in conventional display units using a CRT system,their weight and thickness are becoming problematic with the recentgrowing tendency toward large-sized display screens and there have beenstrong demands for light-weight and thin type display units. As aresult, the development of flat flat-panel displays such as plasmadisplay panels and liquid crystal displays are being actively pursued.

In plasma display panels, color display is obtained by generating plasmaby electrical discharge in rare gas, producing vacuum ultraviolet lightthrough the generated plasma, and causing phosphor materials of 3 pixelcolors, R, G and B, to emit light by the vacuum ultraviolet excitation.

In liquid crystal displays, on the other hand, since they are not selfluminous type of displays, reflection type displays, which use externallight, and backlight type displays, which use back light on the backside of liquid crystal, are used. In large-sized liquid crystaldisplays, however, backlight type is commonly used. To provide colordisplay, a backlight emits white light, which contains R, G and B light,from the back side of a liquid crystal device and a color filterseparates the white light transmitting the liquid crystal device into R,G and B.

The phosphor materials used in the plasma display panels and backlightsof liquid crystal displays are also required to have opticalcharacteristics such as luminance, chromaticity and aging characteristicof the same.

Japanese Patent Laid-Open No. 2003-297291 discloses cerium,terbium-doped lanthanum phosphate (LaPO₄: Tb, Ce) and terbium-dopedmagnesium cerium aluminate (CeMgAl₁₁O₁₉: Tb) phosphor materials as greenphosphor materials whose emission peak wavelengths are at 505 to 535 nm.

Further, Japanese Patent Laid-Open No. 2003-96448 discloses aluminumborate green phosphor materials represented by the formula:Y_(1-a-b)Gd_(a)Tb_(b)Al₃(BO₃)₄ (0.3≦a≦0.55, 0.003≦b≦0.44) which havehigh luminance and are low in decrease of luminance due to theirexposure to plasma.

Fluorescent lamps using xenon discharge, which have lately attractedconsiderable attention as mercury-free fluorescent lamps, are poor inenergy conversion efficiency compared with fluorescent lamps usingmercury discharge. To use them in household applications, they arerequired to have high luminance. If the luminance of xenon fluorescentlamps is increased to the same level as that of mercury fluorescentlamps and is put to practical use, power consumption can be reduced.Thus, it is indispensable to increase the luminance of phosphormaterials.

Plasma displays and liquid crystal displays are alternatives to cathoderay tubes. To allow them to be used in homes, they are also required tohave high luminance. However, in plasma display panels in current use,it is hard to say that they have luminance that fully meets such arequirement. In liquid crystal displays, since their luminance isobtained from their backlights, the requirement can be met by increasingthe luminance of the backlights. However, from the viewpoint of powerconsumption, there have been demands for more efficient and thinnerliquid crystal displays. Thus, it is indispensable to increase theluminance of fluorescent tubes which enable the easy formation of flatlight-emitting devices.

Meanwhile, there have been strong demands for higher luminance andhigher color purity of the green phosphor materials shown in thedescription of prior art.

Demands for increase in luminance and improvement in color purity areparticularly noticeable in plasma display panels. This may have to dowith the fact that the system of TV broadcasting is moving toward theHi-Vision digital production system from the conventional NTSC system.The Hi-Vision digital production system requires 1920×1080 pixels FullSpec; however, the current 37″ to 42″ plasma display panels have only1024×768 pixels. And if plasma display panels are produced whilemaintaining the current pixel sizes, the resultant panels are 55″ to 63″ones. For around 40″ plasma display panels, which are of size commonlyused in homes, to comply with the standard of Hi-Vision full spec, it isnecessary to decrease the pixel size to ⅔ or less of the current one. Ifthe pixel size is decreased to ⅔ of the current size, the luminance ofthe phosphor materials is required to be 1.5 times or more as much asthat of the current luminance. Thus, it is indispensable to increase theluminance of the phosphor materials.

There also exists a problem of color purity with conventional phosphormaterials. For example, when the green phosphor materials have blue- orred-emission, color impurity may occur.

This invention is intended to provide phosphor materials that overcomethe above described problems.

SUMMARY OF THE INVENTION

This invention is intended to provide vacuum ultraviolet excited greenphosphor materials that include terbium, gadolinium-doped rare-earthaluminum scandium borate represented by the following general formula:(Y_(1-x-y)Gd_(x)Tb_(y))Al_(3-z)Sc_(z)(BO₃)₄ (0≦x<0.5, 0<y<0.5, 0<z≦3).

This invention is also intended to provide ultraviolet fluorescentlight-emitting devices including: a light-transmitting sealed container;a discharge medium sealed into the above light-transmitting sealedcontainer for emitting vacuum ultraviolet light; discharge electrodes;and a phosphor layer formed on the inside of the abovelight-transmitting sealed container, characterized in that the phosphorlayer contains a vacuum ultraviolet excited green phosphor material thatincludes terbium, gadolinium-doped rare-earth aluminum scandium boraterepresented by the following general formula:(Y_(1-x-y)Gd_(x)Tb_(y))Al_(3-z)Sc_(z)(BO₃)₄ (0≦x<0.5, 0<y<0.5, 0<z≦3).This invention is also intended to provide white light emitting devicesincluding: a light-transmitting sealed container; a discharge mediumsealed into the above light-transmitting sealed container for emittingvacuum ultraviolet light; discharge electrodes; and a phosphor layerformed on the inside of the above light-transmitting sealed container,characterized in that the above phosphor layer contains; a vacuumultraviolet excited green phosphor material that includes terbium,gadolinium-doped rare-earth aluminum scandium borate represented by thefollowing general formula: (Y_(1-x-y)Gd_(x)Tb_(y))Al_(3-z)Sc_(z)(BO₃)₄(0≦x<0.5, 0<y<0.5, 0<z≦3); a vacuum ultraviolet excited blue phosphormaterial; and a vacuum ultraviolet excited red phosphor material.

The phosphor materials of this invention can provide for more efficientgreen-emitting light sources than any one of conventional ones. Table 1shows that in the relative integrated luminosity when excited by vacuumultraviolet light (wavelength 172 nm) using xenon molecule discharge,the phosphor materials are highly efficient. If used in combination withconventional blue phosphor materials (for example, BAM phosphormaterial) or red phosphor materials (for example, Y₂O₃: Eu, (Y, Gd)BO₃:EU), the phosphor materials of this invention can be provided as highlyefficient white light source.

As is apparent from the values of the chromaticity coordinates shown inTable 1, the color purity of green is better in the phosphor materialsof this invention than in conventional green phosphor materials. This isattributed not only to the green light emission at 540 to 550 nm, butalso to the fact that blue light emission at around 480 to 500 nm andred light emission at wavelength range longer than 575 nm are weakcompared with conventional phosphor materials. Accordingly, displayunits, such as plasma display panels, having good color purity of thegreen color, compared with conventional ones, can be provided.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the emission spectra at wavelengths ofexamples 1 to 8 and comparative examples 1 and 2 of this invention.

FIG. 2 is a graph showing the relative luminescence intensity of thephosphor materials of this invention versus the concentration of dopedSc.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

After intensive research effort, the inventors of this invention foundthat doping gadolinium (Gd) and terbium (Tb)-doped YAl₃(BO₃)₄ crystalwith scandium (Sc) in place of a portion of the aluminum (Al) yieldsphosphor materials that are superior as substitutes for LAP phosphormaterials, and they have accomplished this invention. Green luminescenceof the phosphor materials of this invention occurs at 540 nm to 550 nm,as shown in FIG. 1. Referring to FIG. 2, it is apparent that doping withscandium for aluminum improves the peak luminescence intensity by up to26%, compared with the phosphor material,(Y_(0.55)Gd_(0.25)Tb_(0.2))Al₃(BO₃)₄, of comparative example 2. Further,FIG. 2 and Table 1 show that doping Sc improves the luminance of thephosphor materials by about 24%.

The phosphor materials as above are applicable to the followingproducts.

1. Fluorescent tube lamps using xenon discharge, which include: a glasstube; a rare gas such as xenon sealed into the glass tube; and thephosphor materials coated on the inner walls of the glass tube.

If the phosphor materials are mixed with blue phosphor materials (forexample, BAM phosphor material) and red phosphor materials (for example,Y₂O₃: Eu, (Y, Gd)BO₃: Eu) which emit light efficiently when exposed tovacuum ultraviolet light and coated on the inside of the glass tube,optimum white fluorescent lamps are produced.

2. Flat fluorescent lamps using xenon discharge, wherein the glass tubeof the above products is replaced with sheet-like flat glass.

3. Green pixels of plasma display panels.

EXAMPLES

The vacuum ultraviolet excited phosphor materials of this invention willbe described in detail which include terbium, gadolinium-dopedrare-earth aluminum scandium borate represented by the following generalformula: (Y_(1-x-y)Gd_(x)Tb_(y))Al_(3-z)Sc_(z)(BO₃)₄ (0≦x<0.5, 0<y<0.5,0<z≦3).

First, the method will be described of producing the vacuum ultravioletexcited phosphor materials of this invention which include terbium,gadolinium-doped rare-earth aluminum scandium borate represented by thefollowing general formula: (Y_(1-x-y)Gd_(x)Tb_(y))Al_(3-z)Sc_(z)(BO₃)₄(0≦x<0.5, 0<y<0.5, 0<z≦3).

First, yttrium compounds such as yttrium oxide, gadolinium compoundssuch as gadolinium oxide, terbium compounds such as terbium oxide,aluminum compound such as aluminum oxide, scandium compounds such asscandium oxide, and boron compounds such as boron oxide are used asphosphor raw materials, the raw materials are weighed and picked inaccordance with the compositional formula, and blended well by wet ordry blending.

The blend is filled into a heat-resistant receptacle such as an aluminaor platinum crucible and pre-fired at 400 to 600° C. in the atmosphere.Then, the pre-fired blend is fired at 900 to 1200° C. in the atmospherefor 3 to 20 hours, and the resultant fired product is grinded, washed,dried and sieved to yield a phosphor material of this invention. Thepre-firing and final-firing may be carried out in an acidic atmosphere.And the resultant phosphor material may be re-fired.

The compositions and the relative intensity percentages of the phosphormaterials are shown in Table 1. The phosphor material of sample No. 1will be described by way of an example. The phosphor material wassynthesized as follows.

First, 1.218 g of Y₂O₃ (Kojundo Chemical Lab. Co., Ltd.), 0.889 g ofGd₂O₃ (Kojundo Chemical Lab. Co., Ltd.), 0.733 g of Tb₄O₇ (KojundoChemical Lab. Co., Ltd.), 2.900 g of Al₂O₃ (Kojundo Chemical Lab. Co.,Ltd.), 0.135 g of Sc₂O₃ (Kojundo Chemical Lab. Co., Ltd.) and 2.730 g ofB₂O₃ (Kojundo Chemical Lab. Co., Ltd.) were weighed, fully and uniformlyblended, filled into an alumina crucible and pre-fired in the atmosphereat 50° C. for 2 hours. The pre-fired blend was heated to 1100° C., firedin the atmosphere for 5 hours, and annealed to yield a fired product.The resultant fired product was ground, washed, dried and sieved toyield a phosphor material, Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(2.9)Sc_(0.1)(BO₃)₄.

The phosphor materials of examples 1 to 8 were obtained in accordancewith the above described method, while varying the percentages of Y, Gd,Tb and Sc. The percentages of luminance, the percentages of peakluminescence intensity and the CIE chromaticity coordinates (x/y) areshown for the phosphor materials of examples 1 to 8, LaPO₄: Tb, Ce[LAP], as comparative example 1, and Y_(0.55)Gd_(0.25)Tb_(0.2)Al₃(BO₃)₄, as comparative example 2. The percentages of the luminance ofexamples 1 to 8 and comparative example 2 are percentages of theluminance of comparative example 1 and the percentages of peakluminescence intensity of examples 1 to 8 and comparative example 2 arepercentages of the peak luminescence intensity of comparative example 1.

The measurement of luminance was performed by exposing the phosphormaterials to ultraviolet radiations with a xenon lamp wavelength of 172nm in a bath of nitrogen atmosphere and using a spectrometer, PMA-11, byHamamatsu Photonics K.K in accordance with the measuring methodspecified by CIE (Commission Internationale de i'Eclairage).

TABLE 1 Percentage of CIE Percentage Peak Chromaticity of LuminescenceCoordinates Composition Luminance Intensity x/y Example 1Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(2.9)Sc_(0.1)(BO₃)₄ 106% 92% 0.326/0.593Example 2 Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(2.5)Sc_(0.5)(BO₃)₄ 108% 91%0.324/0.596 Example 3 Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(2.0)Sc_(1.0)(BO₃)₄107% 88% 0.324/0.601 Example 4Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(1.5)Sc_(1.5)(BO₃)₄ 110% 89% 0.324/0.605Example 5 Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(1.0)Sc_(2.0)(BO₃)₄ 109% 95%0.324/0.609 Example 6 Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(0.5)Sc_(2.5)(BO₃)₄108% 97% 0.325/0.611 Example 7Y_(0.55)Gd_(0.25)Tb_(0.2)Al_(0.1)Sc_(2.9)(BO₃)₄ 107% 99% 0.325/0.614Example 8 Y_(0.55)Gd_(0.25)Tb_(0.2)Sc₃(BO₃)₄ 107% 97% 0.324/0.616Comparative LaPO₄:Tb, Ce [LAP] 100% 100%  0.335/0.587 Example 1Comparative Y_(0.55)Gd_(0.25)Tb_(0.2)Al₃(BO₃)₄  86% 73% 0.328/0.592Example 2

As shown in FIG. 1, the phosphor materials of examples 1 to 8 of thisinvention emit light at 540 nm to 550 nm. FIG. 2 shows that doping thealuminum with scandium improves the peak luminescence intensity by up to26%, compared with the phosphor material,(Y_(0.55)Gd_(0.25)Tb_(0.2))Al₃(BO₃)₄, of comparative example 2. Further,FIG. 2 and Table 1 show that doping Sc improves the luminance of thephosphor materials by about 24%.

The phosphor materials of this invention can be used for vacuumultraviolet excited light-emitting devices. The vacuum ultravioletexcited light emitting devices are made up of: a light-transmittingsealed container; a discharge medium sealed into the abovelight-transmitting sealed container for emitting vacuum ultravioletlight; discharge electrodes; and a phosphor layer formed on the insideof the above light-transmitting sealed container. The phosphor materialsof this invention can be used for the phosphor layer. Today, fluorescentlamps and plasma display panels are well known as vacuum ultravioletexcited luminescent devices.

There are disclosed details of well known structures of fluorescentlamps in Japanese Patent Laid-Open No. 2001-172624 etc., but thestructures of fluorescent lamps are not limited to the above ones.

There are disclosed details of structures of plasma display panels inJapanese Patent Laid-Open No. 2003-50561, but the structures of plasmadisplay panels are not limited to the above ones.

In plasma display panels, each pixel emits R, G or B light, and thus thephosphor materials of this invention are used independently. Influorescent lamps, when used for green lamps, the phosphor materials ofthis invention are also used independently. However, when used for whitefluorescent lamp, the green phosphor materials of this invention areused in combination with blue phosphor materials (for example, BAMphosphor material) and red phosphor materials (for example, Y₂O₃: Eu,(Y, Gd)BO₃: Eu) to form a phosphor layer as a blend of the phosphormaterials.

1. A method of producing a vacuum ultraviolet phosphor materialcomprising: providing phosphor raw materials selected from the groupconsisting of yttrium (Y) compounds, gadolinium (Gd) compound, terbium(Tb) compounds, aluminum (Al) compounds, scandium (Sc) compounds, andboron (B) compounds; blending the phosphor raw materials to provide ablended material; pre-firing the blended material to provide a pre-firedmaterial; and firing the pre-fired material to provide a fired materialhaving the following formula:(Y_(1-x-y)Gd_(x)Tb_(y))Al_(3-z)Sc_(z)(BO₃)₄(0<x<0.5, 0<y<0.5, 0<z≦3). 2.The method of producing a vacuum ultraviolet phosphor material accordingto claim 1, further comprising: pre-firing the blended material at atemperature of from 400 to 600° C.
 3. The method of producing a vacuumultraviolet phosphor material according to claim 2, further comprising:firing the pre-fired material at a temperature of from 900 to 1200° C.4. The method of producing a vacuum ultraviolet phosphor materialaccording to claim 3, wherein the pre-fired material is fired for 3 to20 hours.
 5. The method of producing a vacuum ultraviolet phosphormaterial according to claim 2, wherein the blended material is pre-firedin an acidic atmosphere.
 6. The method of producing a vacuum ultravioletphosphor material according to claim 3, wherein the pre-fired materialis fired in an acidic atmosphere.
 7. The method of producing a vacuumultraviolet phosphor material according to claim 3, further comprising:grinding, washing, drying and sieving the fired material.
 8. The methodof producing a vacuum ultraviolet phosphor material according to claim7, further comprising: re-firing the grinded, washed and dried material.